Technologies for estimating the position of an object using a camera image or radio communication have been extensively studied. The method using the camera can perform distance measurement to the object with high accuracy, and with a plurality of cameras, it is possible to estimate two-dimensional and three-dimensional position of the object. On the other hand, there is a disadvantage of having difficulty in measuring an object far from the camera, and thus, having difficulty in grasping the object even by image processing depending on the situation. With a method using radio communication, it is possible to estimate the position of the object over a wide area and detect an identifier (ID) of the object from the communication content to identify the object. On the other hand, an influence of attenuation, reflection, diffraction in the radio propagation path, an influence of radio circuit distortion, or the like, might increase an error, leading to a disadvantage of having difficulty in performing highly accurate position estimation.
In order to solve this problem, a position estimation technology using both radio communication and camera image has been developed. For example, a mobile body equipped with a global positioning system (GPS) receiver and a camera detects its self-position with high accuracy. The position is estimated by the GPS at a place where GPS reception is available, and the amount of movement is grasped by a camera image to estimate the self-position at a place where GPS reception is unavailable. However, conventional techniques use position estimation results by radio (GPS) in the place where the radio (GPS) can be received, making it difficult to improve estimation errors due to radio (e.g., errors due to propagation path, noise, synchronization errors). Moreover, this technique assumes GPS alone as a radio, making it difficult to be applied in areas where GPS is not available.